While researchers have acknowledged the spatial concentration of HIV risk behaviors, few systematic investigations of the relationship between community characteristics and these behaviors have been undertaken. Rooted in social disorganization theory, the proposed analyses assess the hypothesis that urban poverty and residential instability inhibit the development of socially organized and cohesive communities capable of collectively managing individual level behavior relevant to HIV/STD transmission. Using the 1992 National Health and Social Life Survey and two data sets describing the city of Chicago-the 1994 Project on Human Development in Chicago Neighborhoods Community Survey and the 1995-97 Chicago Health and Social Life Survey-this research will address the following questions: 1. What is the joint distribution of key HIV risk behaviors-specifically, anal sex, ineffective contraception, and alcohol use during sex, and illicit drug use during sex-in the U.S. adult population and the population of a large urban center? Do these activities cluster within the same individuals, partnerships, and sexual events? 2. Are structural features of urban communities-including concentrated disadvantage and residential stability-associated with the individual level likelihood of co-occurring HIV risk behaviors? To what extent does dimensions of community social organization - including the capacity of local residents to intervene collectively to achieve shared goals (informal social control) - mediate the relationship between structural disadvantage and the prevalence of HIV risk behaviors at the individual level? 3. To what extent are neighborhood levels and egocentric social network characteristics relevant to participation in HIV risk behavior? Are neighborhood level social networks differentially consequential for the prevalence of HTV risk behaviors at the individual level depending on the degree of informal social control characterizing the neighborhood? Is neighborhood level social network density differentially consequential for the manifestation of HIV risk behavior depending on the social characteristics of network members or their relationships? For instance, are dense networks among kin differentially consequential for HIV risk behavior when compared with friendship density? The proposed analyses will employ sophisticated statistical techniques and high quality data sources to investigate the distribution and etiology of co-occurring HIV risk behaviors. The combination of data sources on Chicago will offer a rare opportunity to investigate the individual level organization of risk behaviors in neighborhood context.